This specification refers to certain patent references and technical references throughout the description, the disclosures of which are incorporated herein by reference in their entireties.
Due to increasing demands for distributed generation, there has been an increasing amount of research dedicated to building small-scale power generators with high power density. The primary focus of recent research has been on micro-turbines because of their intrinsically high power density, low maintenance, longer lifetime, fuel flexibility, potentially higher efficiency, and more compact form factor.
A significant portion of recent research is focused on improving the overall efficiency of centimeter-scale micro-turbines in converting fuel to useable electric power. See McDonald et al., “Small Recuperated Ceramic Microturbine Demonstrator Concept,” Applied Thermal Engineering 28 (2008), pp. 60-74. Most of these efforts have led to solutions such as ceramic turbine components, high efficiency regenerative heating components, air-powered bearings, and highly complicated component geometries. See Vick et al., “Engine Design Strategies to Maximize Ceramic Turbine Life and Reliability,” Proc. ASME Turbo Expo. GT2011-46784, Vancouver, British Columbia (June 2011). These solutions lead to high costs that make it too expensive for mass adoption of micro-turbine technology as a means of implementing distributed generation.
Another branch of micro-turbine research is focused on the design and manufacturing of millimeter-scale micro-turbines that are constructed out of either metal or silicon. The metal engines are manufactured using micro-machining techniques. See, e.g., Isomura et al., “Development of Micromachine Gas Turbine for Portable Power Generation” The Japan Society of Mechanical Engineers International Journal, Series B, Vol. 47, No. 3 (2011), and Matsuo et al., “Towards the Development of Finger-Top Gas Turbines” Proc. International Gas Turbine Congress, Tokyo, Japan, (November, 2003). The silicon engines are manufactured using semiconductor and micro-electro-mechanical system (MEMS) technologies. (See, e.g., Frechette et al., “High-Speed Microfabricated Silicon Turbomachinery and Fluid Film Bearings” Journal of Microelectromechanical Systems, Vol. 14, No. 1 (February, 2005); U.S. Pat. No. 7,487,641 to Frechette et al., “Microfabricated Rankine Cycle Steam Turbine for Power Generation and Methods of Making the Same”; U.S. Pat. No. 6,392,313 to Epstein et al., “Microturbomachinery”; and U.S. Pat. No. 7,934,368 to Muller et al., “Ultra-Micro Gas Turbine”) Reducing the characteristic length of the engine in this way theoretically increases the power density, but prohibitively expensive manufacturing technologies such as the ones described above are required. See Peirs et al., “A Microturbine for Electric Power Generation” Sensors and Actuators A 113 (2004) pp. 86-93.
Accordingly, there is still a need for a low cost power generator that retains all of the other advantages of a micro-turbine. When considering affordability as another design goal, then it becomes difficult to achieve high efficiencies at the same time using conventional designs. The challenge is, therefore, to find a compromise between cost and efficiency while maintaining low maintenance and a compact form factor. As a consequence of low maintenance requirements, the carbon footprint of a long lived micro-turbine could be 30% less than conventional reciprocating systems due to the reduced demand for lubricating oil—while maintaining comparable efficiencies. This has led to a new concept for designing micro-turbine engines. Furthermore, the new concept can also be applied to designing small-scale fluid control and manipulation devices in general.
In addition to using the micro-turbine as a stand-alone power generator, it is possible to implement the micro-turbine engine as a part of a combined heat and power system for single family homes. By doing so, each household can reduce carbon dioxide emissions by 1 ton per year. (See e.g. Pehnt, “Environmental impacts of distributed energy systems—the case of micro cogeneration.” Environmental Science and Policy. Elsevier, Vol. 11, p 25-37. February 2008.) In addition, micro-turbine engines can use a wider variety of fuels—such as heating oil, ethanol, syngas, and natural gas—with negligible nitrogen and sulfur oxide emissions compared to those produced by fossil fuel power plants. (See e.g. Energy Nexus Group. “Technology characterization—micro-turbines”. USA: Environmental Protection Agency. 2002). It is the opinion of the inventors that this technology will unlock a use case for a low cost prime mover that will enable the micro-CHP market.